Existing systems, such as Westinghouse's Terminal Communications Control Systems (TCCS) for airport traffic control applications, utilize pulse code modulation, time division multiplex (TDM) and digital signal processing. The TCCS system interfaces nine hotlines, thirty-six radios, seven ringdown trunks, six dial trunks, two communication system networks, up to thirty-five dial intercoms, and forty tape recorder channels. In terms of capability, the system is excellent for intended applications. However, the central switching and control equipment of the system consists of six bays of more than fifty cubic feet in volume. And while the size of equipment is not always a determinant of cost, it should be expected that a reduction in size would reduce the cost of manufacture, apart from other costs associated with the space occupied by the equipment.
In addition to disadvantages of size and cost, prior art systems are not easily expandable and the initial capital investment is often too high for certain applications. The primary reason for this is lack of modularity in the deisgn of both hard and software. Modularity of hardware and software would also have the advantage of efficient maintainability and easy expandability. System design would be simplified and reliability improved by means of multiple redundant modules at the interfaces. Continuous self checking should be used throughout. The core of a system ought to be a simple (therefore highly reliable) control module with dual redundancy.
Thus, an optimal system design would have the following characteristics:
combine analog/digital techniques; PA1 possess modularity of hard/software; PA1 be continuously self-diagnosing; and PA1 have multiple redundancy. PA1 circuit oriented functions allow incremental additions to the processing power; PA1 flexibility within subsystem elements permits user interface modifications while ensuring continuing system integrity; PA1 system modularity based upon functional bus structures allows system configuration by selection of building blocks; and PA1 functional subsystems obey specific sets of rules thereby reducing development risk. PA1 (a) a central multiple network bus; PA1 (b) common control means; PA1 (c) a plurality of interface means for interfacing at least one operator position terminal and a plurality of auxiliary circuit terminations to one another and with said common control means; PA1 (d) said central multiple network bus interconnecting said plurality of interface means according to periodically generated address codes; and PA1 (e) said plurality of interface means providing time division multiplexed representations of the associated auxiliary circuit termination on said central multiple network bus for direct access thereto by the other interface means.
Such a system is a flexible compromise. As will be seen from the details of the invention hereinafter described, the features and associated advantages of this system are: